Why blend colors in OKLCH instead of RGB?

Blending colors directly in sRGB produces muddy midpoints. Mixing a vivid blue and a vivid yellow through sRGB often yields a grey-green that looks dull and unpredictable. This happens because sRGB is not perceptually uniform — equal numeric steps do not correspond to equal perceived differences. OKLCH (and its sibling OKLab) are designed differently: equal numeric steps correspond to equal perceived differences, so midpoints look like what your eye actually expects.

This matters most when you are generating gradients, palettes, or smooth transitions between colors. The perceptual improvement is often dramatic.

The Difference in Practice

require 'abachrome'

blue   = Abachrome.from_hex('#0066ff')
yellow = Abachrome.from_hex('#ffcc00')

# Blend in sRGB (default for most libraries)
rgb_mid = blue.blend(yellow, 0.5)
puts Abachrome::Outputs::CSS.format(rgb_mid)   # => muddy green-grey

# Blend in OKLCH for a perceptually uniform midpoint
blue_lch   = blue.to_oklch
yellow_lch = yellow.to_oklch
lch_mid    = blue_lch.blend(yellow_lch, 0.5)
puts Abachrome::Outputs::CSS.format(lch_mid)   # => vibrant, balanced midpoint

The extra two lines — converting to OKLCH before blending — produce a fundamentally better result. The midpoint color has the brightness and vibrancy you would expect from combining those two colors.

Generating a Gradient Palette

require 'abachrome'

start_color = Abachrome.from_oklch(0.55, 0.22, 30)   # warm orange
end_color   = Abachrome.from_oklch(0.55, 0.22, 270)  # cool blue

palette = Abachrome::Palette.new([start_color, end_color])
steps   = palette.interpolate(steps: 7)

steps.each do |color|
  puts Abachrome::Outputs::CSS.format(color.to_srgb)
end

Because lightness and chroma are held constant while hue sweeps, every stop in the gradient has the same perceived brightness. That consistency makes OKLCH gradients well-suited for accessible data-visualization color scales, where you need each color to carry equal visual weight.

When RGB Blending Is Fine

Of course, OKLCH blending is not always necessary. Use sRGB blending when you need pixel-perfect reproduction of a design tool’s output, or when the two colors are close together and the perceptual difference would be negligible. The trade-off is predictability vs. perceptual quality — for colors that are far apart in the spectrum, OKLCH generally wins.